This application claims priority on Finnish Application No. 20000495, Filed Mar. 3, 2000, the disclosure of which is incorporated by reference herein.
Not applicable.
The invention concerns control equipment for the headbox tip lath in a paper machine or such and a method for controlling the tip lath.
Traditionally, controlling of the headbox in Z and CD directions has been done by using two separate control mechanisms. Controlling over the whole slice width in the Z direction has been done by opening the top lip articulated to the frame. On the other hand, profiling in the CD direction has been done by bending the continuous tip lath by control spindles located at approximately 100 mm intervals.
Controlling in the Z direction of the lip slice is mainly needed in grade changes. However, performed research shows that there is no great need of control in the Z direction. At dilution headboxes CD control of the slice has mainly been used for zeroing of the lip before the start and in some cases for optimising the fiber orientation.
The inventive idea is to divide the traditional tip lath control into two separate control steps: into fine and rough control respectively. Hereby lip zeroing may be done before the start by using fine control, whereas the rough control may be used for doing a sufficient total lip slice control as well as orientation profiling in the CD direction on a larger scale.
The solution allows omitting the joint between the top lip and the top frame, whereby the top lip can be integrated directly into the top frame. In this way the headbox structure is made considerably steadier and simpler. In present day headboxes, the lip slice is controlled by turning the top lip beam with the aid of worm gear reducers around a joint located at the back edge of the top lip beam. Forces applying to the control spindles of the tip lath and to their driving gears become strong due to the large pressure surface area of the top lip beam. The internal headbox pressure is directly proportional to the running speed square, whereby in new high-speed machines structures can no longer be made durable or possible structural solutions are heavy and expensive. In a two-step tip lath control, where the top lip beam of the headbox is fixed, only the pressurized bottom edge of the tip lath will bring about loading of gears and spindles. Hereby the necessary supporting forces also remain small. According to preliminary estimates, considerable savings are achieved in mechanical manufacturing costs in the case of a full-width headbox. On the other hand, strengthening of the framework allows increasing the headbox speed.
In the solution, the tip lath is zeroed by such second actuators attached to the lath, which may be fine control spindles (with a division of e.g. about 100 mm). In each control spindle there is an own independent spindle length control gear V1, V2 . . . The gear may be e.g. an advantageous turnbuckle screw mechanism. Since usually the headbox lip needs zeroing only once during the useful life of the headbox, a motor is not necessarily needed in the fine control. All fine control spindles are attached directly or by intermediate parts at one end to an intermediate part extending over the headbox width, preferably to a beam, which for its part can be moved and bent by rougher first actuators, that is, by rough control actuators located with a division of e.g. 1000 mm CD. The beam is supported in such a way in the frame that it can bend and move in the control direction only. The beam must be so strong that it is able without bending to carry all loads arriving from the tip lath and the fine control spindles. Correspondingly, the rough control actuators must be so strong that they can be used for controlling the lip slice in the Z direction and for bending the beam extending through the machine in this way to control the fiber orientation in the CD direction.
Using the solution it is possible to correct an orientation profile error at a sufficient level using a smaller number of actuators and automation cards. With a full-width machine, this means a saving in actuators and automation as well as a considerably speedier control.
With the proposed solution it is possible to implement a lip slice control that will not change the discharge angle of departure. Thus, the headbox need no longer be tilted to direct the discharge into the jaw between wires when modifying the lip slice size. Correspondingly, horizontal transfer of the top lip is also eliminated.
This application thus proposes a two-step tip lath control for use, whereby two actuators are used, first actuators and second actuators, which are located functionally after one another in a mutual series. The first actuators affect a bent intermediate part, for example, a beam structure, and with the aid of the said first actuators rough control of the tip lath is performed and e.g. the fiber orientation profile is affected. The second actuators may simply be fine control spindles and they are located with a closer division after the first actuators affecting in between the flexible beam and the tip lath, and with the aid of these fine control of the tip lath is performed as well as e.g. zeroing of the tip lath.
Thus, as explained above, the headbox according to the invention may be used in such an application, where the top lip is not articulated, whereby no such forces are applied to the tip lath and the gearbox as in an articulated structure turning at its top lip. However, the invention is also suitable for use in such headboxes, where the top lip beam is articulated to turn.
In state-of-the-art structures, the fiber orientation control is implemented with the aid of fine control spindles located with an approximate division of 100 mm. In the structure according to the invention, the control actuators used for controlling the fiber orientation, that is, the first actuators, are located with a division of approximately 1.0 m only. Equipment thus remains small.
The control equipment for the headbox tip lath in a paper machine or board machine according to the invention and the method for tip lath control are characterised by the features presented in the claims.
In the following, the invention will be described with reference to some advantageous embodiments of the invention shown in the figures of the appended drawings, but the intention is not to limit the invention to these embodiments only.